mythomania; compulsive lying; propensity to lie
A psychological or behavioral tendency to tell lies habitually, often without clear motive. The term is somewhat clinical and less common in everyday conversation than 嘘つき癖 or 虚言症.
See also: 虚言症
His compulsive lying cost him the trust of those around him.
People with mythomania sometimes lose the ability to distinguish between lies and truth.
嘘つき is a common, everyday word for a liar or lying. 虚言癖 is a formal, technical term for a compulsive lying tendency, not used for casual accusations.
Compound of 虚言 (kyogen, 'lie, falsehood') and 癖 (kuse/heki, 'habit, tendency'). The reading へき is the on'yomi used in compounds. The term is a Sino-Japanese word likely coined in modern times to describe pathological lying.